The major objective of this research proposal is to obtain data regading intestinal interstitial fluid and colloid osmotic pressures. Each of the foregoing parameters will be measured from single or dual polyethylene capsules chornically implanted in the walls of cat duodenum, jejunum, ileum and colon. These measurements will be done following the intestinal segment's exposure to 1) vasoconstrictors; 2) vasodilators; 3) luminal absorption; 4) luminal secretion; 5) increases in venous outflow pressure; and 6) decreases in arterial perfusion pressure. The behavior of both interstitial fluid and colloid osmotic pressure under the conditions stated will yield important information on the intestinal tissue's compliance and how it may vary not only along the intestinal tract, but also how it varies according tothe physiological or pharmacological stimulus. Additionally, we also look to obtain information regarding the comparison of interestitial protein concentrations as compared to that of lymph derived from the same interstitium, that is, to determine if lymph protein concentration is a true indicator of that found in the interstitium. Finally, we hope to obtain information as to the lymphatic sensitivity; the interstitial fluid pressure required to drive lymph. The interactions of the Starling forces in fluid equilibrium and the prevention of edema are of utmost importance. Two of these forces are the interstitial fluid and colloid osmotic pressures. In the past, and for the intestine, both have been measured indirectly, or calculated from other relationships. The present proposal offers the opportunity to obtain data regarding these two important Starling forces by direct measurement.